Add rule to `suggest` using a global variable for supported cake version

I would like to suggest to add a new rule suggestion (not a warning) to recommend users to use a global variable with the version of cake being targeted/supported.

This variable could then be re-used in the documentation, and for the PackageReference to Cake.Core.

As an example, see my commit here: https://github.com/cake-contrib/Cake.Transifex/commit/31ded53d4c53ed329257b74dde2df4d60058cbb3

If it gets added, it may be something that needs to be done in conjunction with the project @Jericho is working on/maintaining.